In the manufacture of component parts into a finished product, the presence of gaps may occur. In some instances such gaps are undesirable and must be eliminated. Generally, for gaps larger than about 3 mm, solid shims made out of thermoset plastic or prepreg are inserted into the gap. However, for gaps occurring that are smaller than about 3 mm, liquid shims are used. Liquid shims are typically epoxy-based structural adhesive materials that possess high compressive strength when the shims harden or “cure” to their final solid state. For purposes of liquid shims, a high compressive strength is considered to be greater than from about 8000 psi to about 14000 psi at 2% offset and at room temperature. It is understood that shims may be used to account for and fill gaps anywhere there exists a small dimensional mismatch between adjacent parts. Additionally, epoxy or acrylate resins may be used to modify or otherwise “build-up” areas of material surfaces, such as, for example, composite materials.
Traditional epoxy resins, and other adhesive resin curing systems are typically governed by understood curing kinetics. In the case of epoxy resins, the curing of epoxy resin systems is often governed by the curing kinetics of epoxy resins with multifunctional amines or thiol reactive groups that are often combined with a catalyst. Such adhesive systems have limited manufacturing flexibility due to the relationship between pot life and cure time. Pot life is understood to be the amount of time available to make an active epoxy system, and then apply it to the desired end use before the epoxy system “sets” or “cures” to the point where it becomes unworkable to apply (because the epoxy has hardened and will no longer “flow”). Therefore, highly accelerated epoxy resin adhesive system cure times inevitably lead to shorter, and often impractical, pot life times. Conversely, an epoxy resin system having a longer pot life takes a longer time to cure. Longer adhesive system cure times increase manufacturing time on a production line, and otherwise lead increased production inefficiency.
In addition, known epoxy resin- and acrylate resin-based adhesive systems may require heat to activate a system catalyst and “trigger” the curing reaction. In many manufacturing systems for large components, including the aerospace industry, presenting equipment capable of supplying evenly applied heat to such components of a certain dimension to trigger adhesive curing is not possible, not practical, or would significantly increase manufacturing cost.
An efficient and cost-effective on-demand adhesive system that is both rapid curing, and that also has a significantly long pot life would be useful, cost-effective and highly advantageous.